DESCRIPTION (Investigator's Abstract): Despite a century of experimentation and clinical observation, the functional representation within the human motor cortex is still unclear., We propose to address this issue using functional hemoglobin-based magnetic resonance imaging at high magnetic field of 4 Tesla. This non-invasive high resolution technique detects local changes in deoxyhemoglobin, thought to reflect underlying changes in neural activity. The long term objective of this research is to understand the determinants of the volume of functional activation and of the intensity and spatial distribution of that activation in the human motor cortex during the production of motor output. The specific aims of the proposal are: #1 To determine the volume of functional activation in the human motor cortex during movements of varying complexity. The hypothesis to be tested is that the volume of activation is a function of the complexity of the task. #2 To determine if the attem and the intensity of activation in the human motor cortex during movements of the arm and hand, separately and in combination. The hypothesis to be tested is that the spatial distribution of the activation relates to the body part being used and that increased movement complexity is reflected in changes in the spatial distribution or the intensity of this activation. #3 To examine how the hemispheric asymmetry of activation within the 1niman motor cortex relates to handedness and to the type of motor task being performed. The hypothesis to be test that asymmetrical activation reflects both handedness and aspects of the motor task. #4 To determine the volume and pattern of activation within the motor cortex, the anterior motor areas and posterior parietal area during vasomotor mental rotation (a specific form of complex motor behavior). The hypothesis to be tested is that vasomotor mental rotation will include activation within the posterior parietal area. Healthy human subjects, equally divide into groups of right and left handed men and women, will be used in the study. These subjects will perform a series of motor tasks with the right and left, arm and hand separately during multislice functional imaging of the right and left motor cortex. There are three tasks in all, each of which has two components. In general, the amount of muscle activity required for each component within a task will be similar, while the components will differ in complexity. For each subject the volume and the intensity of activation in the motor cortex of each hemisphere will be calculated and its spatial distribution determined, for all task components. Analysis will be confined to within subject comparisons A repeated measures ANOVA will be used to detect task differences in the volume and of intensity of activation, and regression analysis used to relate these differences to measures of task complexity and musc activation. The spatial distribution of activation will be described with reference to standard anatomic landmark differences in this distribution between any two task constructing tested by constructing difference maps.